For the purpose of eliminating nitrogen oxide of an exhaust gas in the engine of a construction machine or the like, the construction machine is provided with a reductant container for supplying a reductant into an exhaust pipe through which the exhaust gas passes. If the reductant container is used in a cold region, there is a possibility that the reductant in the reductant container freezes. In order to cope this situation, the reductant container is equipped with a heating member for unfreezing the frozen reductant by means of heat exchange. This type of reductant container has a container main body for containing the reductant, a heat exchanger for unfreezing the reductant by exchanging heat with the reductant contained in the container main body, a protector disposed to surround the heat exchanger to rapidly unfreeze the reductant around the heat exchanger, and a suction pipe with an inlet port that is located inside the protector and suctions the reductant unfrozen by the heat exchanger (see Japanese Patent No. 3686668, for example). This reductant container has the protector surrounding the heat exchanger so that the reductant around the heat exchanger can be unfrozen rapidly. The reductant unfrozen by the heat exchanger is supplied to the inside of the exhaust pipe through the suction pipe.
The reductant to be supplied to the inside of the exhaust pipe is required to satisfy a predetermined concentration condition. This reductant container has a concentration meter provided inside the protector. When the concentration of the reductant specified by this concentration meter reaches a predetermined value, the reductant is supplied to the inside of the exhaust pipe through the suction pipe. Specifically, in this reductant container, the concentration meter senses the temperature of the reductant in the product and specifies a concentration of the reductant based on the sensed temperature. Then, when the concentration of the reductant specified by the concentration meter satisfies a predetermined concentration condition, a feed device such as a pump supplies the reductant to the inside of the exhaust pipe through the suction pipe. In this reductant container, the reductant in the protector is unfrozen by the heat exchanger, and the temperature of the unfrozen reductant is sensed by the concentration meter, as described above. Consequently, the reductant satisfying the predetermined concentration condition is supplied to the inside of the exhaust pipe.
Incidentally, in the reductant container, even when the temperature of the reductant unfrozen reaches a predetermined temperature around the suction port, the reductant is not supplied to the inside of the exhaust pipe if the temperature of the reductant sensed by the temperature measuring unit is below a predetermined temperature. In other words, in this reductant container, in a case where the temperature of the reductant sensed by the temperature measuring unit is below the predetermined temperature, the temperature of the reductant in the protector is determined as not satisfying the predetermined concentration condition and therefore is not supplied to the inside of the exhaust pipe. However, of the reductant in the protector that is unfrozen by the heat exchanger, when the temperature of the reductant around the temperature measuring unit increases slowly, it takes a certain amount of time for the temperature sensed by the temperature measuring unit to reach the predetermined temperature. Even when the reductant in the protector is unfrozen rapidly by the heat exchanger surrounded by the protector, it takes a certain amount of time from unfreezing the reductant to supplying the resultant reductant so long as the temperature of the reductant around the temperature measuring unit increases slowly.